Many natural gas distribution companies purchase natural gas from gas transmission companies at designated purchase stations, where the amount of natural gas being sold is measured. The natural gas at these purchase stations is heated, measured and reduced in pressure.
Until the late 1970s, archaic orifice meters were used to measure the amount of the gas being transferred from transmission and distribution points. Most of the transfer stations maintained multiple orifice meter runs (supply lines) arranged in parallel. Parallel meter runs were necessary in order to obtain accurate measurements of the gas flow with respect to the measuring instruments' water column range of 0 to 100 inches of water. The measurement was found to be most accurate in the 50-inch (or, the mid-range of differential pressure) measurement. Therefore, gas flowing at 85 inches of water through a primary line, for example, was diverted through a parallel, secondary line. This adjusted the differential pressure in each of the primary and secondary lines to 40 inches of water (the mid-range of the water columns), and avoided exceeding the upper measurement limits of the instruments.
The transmission companies using these multiple run systems typically utilize a constant bleed pneumatic limit flow controller to activate the parallel orifice meter runs
In the late 1970s, the use of liquefied natural gas prompted the transmission companies to install sophisticated electronic measuring devices in order to bill their customers for the amount of energy being transferred in each line, rather than measuring the volume of the flowing fluid.
Today, despite the capability for electronic control and measurement of natural gas at each purchase station, the transfer companies are still using the old-fashioned limit flow control equipment for gaseous natural gas transmission.
In order to regulate the gaseous flow between runs, the current constant bleed pneumatic controllers needlessly waste approximately 1,437 standard cubic feet of natural gas each day that they are in operation, i.e., when both runs are allowing gas to flow therethrough. This mode of operation is most prevalent in the winter months, when there is a greater demand for heating fuels. Although only small amounts of gas are being vented, it has been determined that the cumulative costs are great.
The present invention is a system for replacing the constant bleed pneumatic controllers for these transfer stations, thus providing the means by which substantial savings in fuel and money can be realized.